Clutch systems having an actively closed friction clutch and being actuated by means of a lever are known from DE 10 2004 009 832 A1, as is the basic structure of a lever actuator. In such friction clutches an adjusting means may be present, which compensates abrasion-related axial wear of the friction linings, in that the pressure plate clamping the friction linings against an axially fixed counterpressure plate is spaced by the axial amount of the wear relative to the clamping means, for example a lever or diaphragm spring, by the amount of abrasion of the friction linings. Such an adjusting means consists for example of ramp rings rotatable relative to one another in the circumferential direction, one of which ramp rings is accommodated fixedly in the circumferential direction on the pressure plate or incorporated therein and a ramp ring provided with corresponding counter-ramps is accommodated rotatably on the first ramp ring. If adjustment is initiated, the rotatable ramp ring is rotated to a limited degree. Adjustment is initiated, in the case of the proposed clutch system, by overtravel of the clutch stroke, i.e. the distance traveled by the lever tips or the tips of the clamping means. The overtravel is initiated by an engageable/disengageable stop. In normal operation of the friction clutch, this engageable/disengageable stop forms a stop for the lever of the lever actuator acting on the lever tips of the clamping means. To effect adjustment, in adjusting operation the engageable/disengageable stop is moved away, for example swiveled out, such that the clamping means describes a larger clutch stroke to reach an end stop during an opening process. During the subsequent engaging process of the friction clutch, the increased clutch stroke partially rotates a worm wheel actuated by the overtravel, which worm wheel drives the rotatable ramp ring in the circumferential direction. The engageable/disengageable stop may be controlled automatically by means of a for example electrical actuator, which is controlled by a controller. In this respect, the controller may determine a requirement for adjustment from measured variables of the lever actuator, such as stop positions, actuator currents and/or loads. Alternatively, swiveling out of the engageable/disengageable stop may proceed mechanically when the engage travel of the clamping means is lengthened by a given amount. This is the case in particular when the friction linings have been abraded by a given axial amount.
In order to be able to adapt the lever actuator exactly to the predetermined clutch stroke and the characteristic line underlying actuation of the friction clutch and thus the actuator forces necessary therefore, exact knowledge of the starting points of the characteristic line, and thus of the position of the lever stop, is necessary.